1. Field of the Invention
The present invention relates to a method of adjusting vehicle wheel alignment, and in particular, to a method of adjusting vehicle wheel alignment in which forces, which are generated by a tire when a wheel which is placed on a tire driving surface is rotated by driving/rotating the tire driving surface, are measured, and based on the results of measurement, the positional angle is adjusted so as to improve the running stability of the vehicle and decrease one-sided wear of the tire.
2. Description of the Related Art
In general, tires are provided with a camber angle which ensures the running stability of the vehicle, and are provided with a toe angle for preventing one-sided wear caused by the provision of the camber angle. (Note that in the present application, "one-sided wear" refers to a state in which, when the state of wear of a worn tire is observed, it is noted that the amount of wear from one tread shoulder portion to the other tread shoulder portion varies in a taper shape, i.e., uneven wear in which the amount of wear at one tread shoulder portion is greater than the amount of wear at the central portion of the tread and at the other tread shoulder portion.
Conversely, the tire may be provided with a toe angle which balances the forces generated at the front tires and the rear tires of the vehicle so as to ensure the running stability of the vehicle, and may be provided with a camber angle for preventing one-sided wear caused by the toe angle. Alternatively, the toe angle and the camber angle may both be adjusted in combination in order to optimize the running stability of the vehicle and minimize one-sided wear of the tire in light of limitations of the vehicle such as the structural dimensions and the like.
Accordingly, in order to improve the running stability and the one-sided wear resistance of the tire in a vehicle running state, it is important to adjust the camber angle and the toe angle, which are the positional angles, of each wheel. In conventional methods for adjusting the toe angle and the camber angle, usually, angles and dimensions are measured for each wheel, and the toe angle and the camber angle are adjusted so that the measured angles and dimensions become target values set at the time the vehicle is designed.
Tires have various characteristics such as ply steer which is generated by the internal structure of the tire; toe force which is generated due to the tire having an angle with respect to the proceeding direction of the vehicle because the rotating direction of the wheel and the proceeding direction of the vehicle are different; self-aligning torque caused due to the points to which force is applied in the ground-contacting surface being offset from the proceeding direction; camber thrust generated by the tire deforming due to the camber angle of the wheel, and generated by its relation with the rigidity of the tire due to the internal structure of the tire; camber moment caused by the difference in the length of the ground contacting surface at the left and right sides of the tire; conicity resulting from manufacturing errors in the configuration which are inherent in industrial goods; rolling resistance which depends on the internal structure and the material from which the tire is formed such as rubber; and the like. These characteristics depend on and vary in accordance with the load which is applied to the wheel. Further, these characteristics also vary in accordance with the type of tire.
The aforementioned forces are generated by the deformation of the tire. The force which is generated by the tire in order to make the vehicle run while controlling its running direction is the sum total of the aforementioned forces. Therefore, regardless of the type of tire, the force thus generated in order to make the vehicle run differs in accordance with the load distribution of the vehicle to which the tire is mounted and the positional angle of the wheel to which the tire is mounted. Accordingly, in order to respond to the demands for vehicles' improved ability to travel at higher speeds and the demands for good straight line stability, a method of adjusting the positional angle which results in better running stability and better one-sided wear resistance is needed. However, in order to realize such a method, a method for adjusting the positional angle which is based on the characteristics of the tire must be provided.
The following art is known as a conventional method for adjusting the positional angle which focuses on the characteristics of the tire. A wheel is driven by using a plurality of rollers. The respective forces generated by the rollers are measured, and the toe angle and the camber angle are measured on the basis of the orientations and magnitudes of the measured forces. (Refer to Japanese Patent Application Publication JP-B No. 51-18681.) However, it has been confirmed that the force generated at the time of contact of the tire and the road surface differs in accordance with the configuration of the contact between the tire and the road surface. Because the configuration of the contact between the tire and the rollers differs greatly from the configuration of the contact between the tire and an actual road surface, the characteristics of the generated force also differ greatly on the rollers and on a road surface.
More specifically, the force generated at the time the tire is run on rollers is similar to the force generated at the time the tire is run on an actual road surface with respect to the lateral force caused by the ply steer and the provision of the toe angle. However, the positional angle and the magnitude of the force differ greatly from those in the case in which the tire is run on an actual road surface. Further, the camber thrust can barely be detected. Moreover, the force generated by the tire cannot be detected due to the deformation of the tire caused by the external disturbance resulting from the countless protrusions and recesses existing on an actual road surface.
In the above-described conventional art, the measured force exhibits values which are different than values obtained on an actual road surface. In order to correct the measured values to the values obtained on an actual road surface, data expressing the characteristics of the respective tires on an actual road surface is needed. Therefore, the above-described conventional method lacks wide applicability in actual practice. Further, no technical information has been disclosed with regard to what angle the positional angle should be adjusted to in order to optimize the positional angle.
Further, a technique is known which aims to achieve high running stability by driving a wheel by using a plurality of rollers and bringing the generated lateral force to substantially zero. (Refer to Japanese Patent Application JP-A Laid-Open No. 7-5076.) In this art, when the generated lateral force is to be made zero, a wheel provided with a camber angle is provided with a positional angle which results in the generation of a force in the direction opposite to the direction of the camber thrust.
In this art, the camber thrust can barely be detected because, in the same way as in the previously-described case, the contact surface of the rollers and the tire is different than the contact surface of an actual road surface and the tire. Further, in order to bring the lateral force to zero, the force from the road surface generated by the traveling of the vehicle must be applied in the direction opposite to the direction of the force generated by the wheel, so as to offset the force generated by the rotation of the wheel. In this case, the deformation of the ground-contacting surface of the tire becomes even larger than when the tire is in a stationary state, and this deformation of the ground-contacting surface is a factor in the generation of one-sided wear of the tire.
The inventors of the present invention have filed with the Japanese Patent Office an application JP-A No. 7-139506 related to the present invention, which is still pending and not yet publicly known. The related art proposes a method of adjusting the positional angle of a wheel by rotating the tire on a substantially planar surface by using a belt or the like, detecting the force generated by the wheel, and adjusting the positional angle of the wheel on the basis of the force. However, an actual road surface is formed by countless protrusions and recesses, and during travel, the tire always is deformed and affected by the force generated by contact with the road surface and the force caused by the deformation. The force which can be detected when the wheel is run on a substantially planar surface formed by a belt or the like is only the former force, and therefore, only a portion of the force generated during travel on an actual road surface can be detected. Accordingly, adjusting the positional angle of the wheel on the basis of the force detected when the wheel is run on a substantially planar surface contributes to improving the running stability when the vehicle runs straight on a road surface which is extremely planar, but does not address the other running characteristics nor one-sided wear.
More specifically, when a tire runs on an actual road surface, various forces which are generated in different ways are generated. Although these forces differ in accordance with the characteristics of the tire, the following conventional methods, have been used: (1) a vehicle using specific tires is actually run, the angle at which there is little one-sided wear and running stability does not deteriorate is measured empirically, and the wheel is adjusted to this angle; (2) the force measured with the tire running on a planar surface is offset so as to be adjusted to a minimum value (substantially zero); (3) only a specific force measured with the tire running on a planar surface or on rollers is made to become a minimum value (substantially zero); (4) the angle is adjusted to a value obtained by some method. However, a method which can be used with various vehicles and various tires has heretofore not been realized.